1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor.
In this specification, a semiconductor device refers to all types of devices which can function by utilizing semiconductor characteristics; an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
A technique by which a transistor is formed with a semiconductor thin film formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to the transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor that includes an amorphous oxide semiconductor film containing indium (In), gallium (Ga), and zinc (Zn) is disclosed (see Patent Document 1).